5 ms·

Prior to the Ground Fault Interruptor sockets found in modern bathrooms, an isolating transformer was often used to protect bathroom outlets in the 60s and 70s.

Prior to the Ground Fault Interruptor sockets found in modern bathrooms, an isolating transformer was often used to protect bathroom outlets in the 60s and 70s. These are two-pin unpolarized sockets, usually with "Razors Only" stamped on the front (because if you plug in a 1000 W hair dryer you blow out the transformer).

TazeTSchnitzel 14y ago
I always wondered why it said "Shavers Only". Luckily the worst thing I ever stuck in was an American phone charger.
texec 14y ago
Current installations use Residual-Current Devices instead of individual breakers, at least in Europe. This requires three way wiring up to the distribution. In Germany RCDs are required for all outlets in new installations.
- sc00ter 14y ago
  Or rather both - individual circuits have a current limiting circuit breaker in addition to a master RCD across multiple circuits.
- brudgers 14y ago
  In the US, it is relatively common to use circuit breakers in new construction but in no way universal - protection at the receptacle is still very common and can be significantly cheaper since only the first receptacle in a series needs to be GFCI type...of course this creates an issue of finding the tripped device for a person unfamiliar with the wiring scheme.
- lostlogin 14y ago
  RCDs are required throughout the house in New Zealand now (used to be bathroom only). They work. I tried angle grinding a metal bar, and it's link to the extension cord fell in a puddle I was standing in. Power clicked off thank god, and I became ok with the re-wiring cost. RCDs are the best.
ajasmin 14y ago
Does that mean the output of the transformer have no difference of potential relative to the ground? Why is that? It must be for the same reason that an electric shock from an ungrounded AC circuit doesn't travel through your feet as the article mention. But I'm having difficulties understanding this concept. My (admittedly naive) understanding of electricity is that when one terminal has more electrons than another you can wire both terminals to a light bulb and it will light up. i.e. electron travel through the light bulb from one terminal to the other. If my understanding was correct it would mean that one terminal from the input circuit of the isolation transformer (the neutral wire and the ground it is connected to) would always have the same number of electrons than either terminal of the transformer output. Since the reason we have an isolation transformer is to prevent electrons from traveling between the transformer output and the ground, both outputs and the ground need to have the same number of electron. i.e. zero voltage. Right? Is there really no voltage at all between the two circuits? I find this confusing.
- jakobe 14y ago
  You must understand the concept of capacity: Capacity describes the amount of charge (number of electrons) needed to create a potential difference (voltage) across a gap. The capacity between ground and shaver circuit is tiny, so only a really tiny number of electrons travels through you to put the shaver circuit on the same potential as ground. The important thing here is that as soon as you ground the shaver circuit by touching it, there is a (tiny) static discharge, and then there is no force that restores any potential difference between ground and shaver circuit. The only force is the transformer, creating a potential difference between the two ends of the shaver circuit. But since that circuit is open, and again has a low capacity, barely any electrons need to move in order to create that potential difference.
- andrewreds 14y ago
  Ummm.... Essentially electrons must travel around in a circuit. Sort of like a racing car. Electrons can't teleport from one location to another, and the number of electrons in a circuit will never change. If touching you touch a wire, and you don't make a circuit (a complete loop) then you will receive no current (electrons can't move in a circuit), thus there is no voltage (since V = IR) Usually when you touch the active wires in a powerpoint a circuit is made: from the powerplant to the powerpoint, from the powerpoint to you, from you to the floor you are standing on, from the floor back to the powerplant. A transformer works by having two coils of wires, and when electrons flow through one coil, it excites the electrons in the other coil, and they start to move too. (This is done through magnetism). A transformer is usually used to change the voltage of an AC source, but in the case of the "Isolation transformer" the voltage on the input side and the output side are the same. In a transformer, the two coils of wire aren't actually connected to each other. So if you touch one of the output wires, you don't make a circuit, as the electrons need to get back to the other output wire for a circuit to be formed. The same thing happens with a battery. Unless you are touching both terminals, there will be no current flow.

TazeTSchnitzel 14y ago

I always wondered why it said "Shavers Only". Luckily the worst thing I ever stuck in was an American phone charger.

texec 14y ago

Current installations use Residual-Current Devices instead of individual breakers, at least in Europe. This requires three way wiring up to the distribution. In Germany RCDs are required for all outlets in new installations.

sc00ter 14y ago
Or rather both - individual circuits have a current limiting circuit breaker in addition to a master RCD across multiple circuits.
brudgers 14y ago
In the US, it is relatively common to use circuit breakers in new construction but in no way universal - protection at the receptacle is still very common and can be significantly cheaper since only the first receptacle in a series needs to be GFCI type...of course this creates an issue of finding the tripped device for a person unfamiliar with the wiring scheme.
lostlogin 14y ago
RCDs are required throughout the house in New Zealand now (used to be bathroom only). They work. I tried angle grinding a metal bar, and it's link to the extension cord fell in a puddle I was standing in. Power clicked off thank god, and I became ok with the re-wiring cost. RCDs are the best.

ajasmin 14y ago

Does that mean the output of the transformer have no difference of potential relative to the ground? Why is that? It must be for the same reason that an electric shock from an ungrounded AC circuit doesn't travel through your feet as the article mention. But I'm having difficulties understanding this concept. My (admittedly naive) understanding of electricity is that when one terminal has more electrons than another you can wire both terminals to a light bulb and it will light up. i.e. electron travel through the light bulb from one terminal to the other. If my understanding was correct it would mean that one terminal from the input circuit of the isolation transformer (the neutral wire and the ground it is connected to) would always have the same number of electrons than either terminal of the transformer output. Since the reason we have an isolation transformer is to prevent electrons from traveling between the transformer output and the ground, both outputs and the ground need to have the same number of electron. i.e. zero voltage. Right? Is there really no voltage at all between the two circuits? I find this confusing.

jakobe 14y ago
You must understand the concept of capacity: Capacity describes the amount of charge (number of electrons) needed to create a potential difference (voltage) across a gap. The capacity between ground and shaver circuit is tiny, so only a really tiny number of electrons travels through you to put the shaver circuit on the same potential as ground. The important thing here is that as soon as you ground the shaver circuit by touching it, there is a (tiny) static discharge, and then there is no force that restores any potential difference between ground and shaver circuit. The only force is the transformer, creating a potential difference between the two ends of the shaver circuit. But since that circuit is open, and again has a low capacity, barely any electrons need to move in order to create that potential difference.
andrewreds 14y ago
Ummm.... Essentially electrons must travel around in a circuit. Sort of like a racing car. Electrons can't teleport from one location to another, and the number of electrons in a circuit will never change. If touching you touch a wire, and you don't make a circuit (a complete loop) then you will receive no current (electrons can't move in a circuit), thus there is no voltage (since V = IR) Usually when you touch the active wires in a powerpoint a circuit is made: from the powerplant to the powerpoint, from the powerpoint to you, from you to the floor you are standing on, from the floor back to the powerplant. A transformer works by having two coils of wires, and when electrons flow through one coil, it excites the electrons in the other coil, and they start to move too. (This is done through magnetism). A transformer is usually used to change the voltage of an AC source, but in the case of the "Isolation transformer" the voltage on the input side and the output side are the same. In a transformer, the two coils of wire aren't actually connected to each other. So if you touch one of the output wires, you don't make a circuit, as the electrons need to get back to the other output wire for a circuit to be formed. The same thing happens with a battery. Unless you are touching both terminals, there will be no current flow.